In the automatic testing of electrical circuits, test probes are used in groups of hundreds or thousands to contact test points of an electrical circuit under test. Such test probes are inserted into receptacles which are in turn inserted into a test fixture and connected by individual wires to diagnostic equipment. The diagnostic equipment routes computer generated test routines through the test probes to the circuit under test to determine continuity and identify failure in the circuit. One such type of test probe is a spring-loaded test probe.
Conventional spring-loaded test probes generally include an elongated tubular barrel, an elongated plunger, and a spring. The barrel consists of an elongated body having an inner bore, a generally closed end, and an open end. The plunger is slidably mounted within the open end of the barrel and extends outwardly therefrom for contacting a test point of the circuit under test. The spring is seated in the generally closed end of the barrel and is interposed between the barrel and the plunger for biasing the plunger axially and outwardly of the barrel.
In such spring-loaded test probes, the plunger is retained within the spring-loaded barrel by means of either a dimple crimp or a spin crimp. That is, upon assembly of the probe, the plunger is inserted into the open end of the spring-loaded barrel, and tooling and precision machines are then used to form either a dimple crimp or a spin crimp in the body of the barrel to retain the plunger within the barrel. As such, approximately 600 probes per hour can be assembled using the spin crimp method, and approximately 1000 probes per hour can be assembled using the dimple crimp method. Thus, such spring-loaded test probes are not fully satisfactory because they involve a method of assembly which requires tooling and precision machines to form crimps in the body of the barrel, and also because they provide for a relatively low rate of assembly.
In addition, the barrels of such spring-loaded test probes are typically formed of alloys which cannot be heat treated prior to assembly. As is known in the art, heat treating the barrel of a test probe has the dual advantage of hardening and lengthening the life of the barrel, as well as increasing the conductivity of the barrel. However, if the barrels of such spring-loaded test probes were heat treated prior to assembly, the barrels would fracture upon formation of the crimp due to the hardness of the barrels. Thus, such spring-loaded test probes are also not fully satisfactory because they involve a method of assembly which is not conducive to the use of a heat treated barrel.